Intangible Assets - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Finite lived intangible assets gross		$ 2,585
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets		7	$ 7	$ 7
Current alternative or renewable energy credits		5	4
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Current alternative or renewable energy credits		251	191
Alternative Or Renewable Energy Credits Noncurrent		56	44
PECO Energy Co [Member]
Goodwill [Line Items]
Current alternative or renewable energy credits		2	13
Unamortized Energy Contracts [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	22	135	430
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]		0	0
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	22	135	507
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	0	$ 0	$ 0
Constellation Energy Group LLC [Member] | Unamortized Energy Contracts [Member]
Goodwill [Line Items]
Finite lived intangible assets gross	[2],[3]	$ 1,499
Constellation Energy Group LLC [Member] | Trade Names [Member]
Goodwill [Line Items]
Useful life		10 years
Finite lived intangible assets gross	[3]	$ 243

[1] Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[2] Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $44 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $3 million, $0 million, $2 million, $3 million and $4 million for 2016, 2017, 2018, 2019 and 2020, respectively.

[3] On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations.